The Upscale Praetor was a fun build, and yes....the fins are ginormous.

I used a carbon fiber / kevlar honeycomb sheet to make the fins. The edges are framed in basswood. I still have some of the composite scrap material....I'll see if I can find it and post a pic. Lightweight and super strong. You can hear them whistle when the motor burns out....too cool.

I've actually thought of doing a 4" upscale Praetor. That would put the fin "span" at 36" if I remember correctly....maybe more. I'll have to think of a clever way to break it down because with fins that long I'd never be able to transport it easily.